Multi-turn potentiometer



Feb. 13, 1962 F. R. PERIER ETAL 3,021,494

MULTI-I'URN POTENTIOMETER Fi led Aug. 5, 1-960 2 Sheets-Sheet 1 M M MYM AIIORNEYS Feb. 13, 1962 F. R. PERIER ETAL 3,02

MULTI-TURN POTENTIOMETER Filed Aug. 5, 1960 2 Sheets-Sheet 2 VENTORS FRANK R. P RIER BfNGELO DI BELLA ATIOR N EYS United States Patent O 3,021,494 MULTl-TURN POTENTIOMETER Frank R. Perier and Angelo Di Bella, Tucson, Ariz., assignors to Acton Laboratories, Inc., Acton, Mass, a corporation of Massachusetts Filed Aug. 5, 1960, Ser. No. 47,691 16 Claims. (Cl. 338-148) This invention relates to rotary otentiometers and more particularly to rotary potentiometers of the type having a multi-turn helical resistance element and a rotatable contact which rides along the turns of the resistance element. 7

Multi-turn potentiometers are well known and have achieved substantial acceptance. However,-there has existed the need for a relatively inexpensive multi-turn precision potentiometer. Heretofore, it has been customary to insert a helical resistance element within a casing formed in two identical halves or, alternatively, to mold a plastic housing around the resistance element. The former approach suffers from the disadvantage that the operating shaft of the potentiometer is weakly mounted and is susceptible to misalignment on initial installation. Some strengthening is achieved by supporting the operating shaft in both ends of the housing. However, this is unsatisfactory in certain situations since it complicates the operating mechanism of the potentiometer which is disposed within the casing. The alternative approach of molding a casing around, the resistance element has the disadvantage that it requires a complicated mold which is expensive and'diflicult to maintain in perfect working order.

Accordingly, the primary object of the present invention is to provide a relatively inexpensive multi-turn precision potentiometer which has most of the advantages and substantially none of the disadvantages of multi-turn potentiometers of the type heretofore known and available.

A more specific object of the present invention i to I provide a multi-turn potentiometer comprising a novel casing formed in two halves, with one half having means for supporting the operating shaft of the potentiometer without assistance from the other half of'the casing.

A more specific object of the present invention is to provide a multi-turn potentiometer comprising a helical resistance element disposed in a casing formed in two parts, one part having an end wall which includes a major portion substantially equal to one half of the crosssectional area of the completed casing and a second minor portion which cooperates with the first major portion to define an opening in which the operating shaft of the potentiometer may be mounted, the other half of the casing having an end wall which is substantially less than one half the cross-sectional area of the completed casing, the end wall of said other half being cut away so as to be complementary to the minor portion of the end wall of the first half of the casing.

. Still another object of the present invention is to providea multi-turn potentiometer having a helical resistance element, said potentiometer comprising a casing formed in two parts, one end of said casing being open, and further including a removable cover member'which can be screw-threaded into cooperating relation with the casing whereby to close its open end.

Still a further specific object is to provide a multi-turn potentiometer having a new, Simple and inexpensive operating assembly which comprises an operating shaft rotatably mounted in a supporting stationary bushing, a nut screwed onto said bushing, a contact member carried by said nut and moveable along the turns of the resistance element of the potentiometer as the nut is rotated on said bushing, and a. U-shaped yoke carriediby said shaft for rotatingsaidnut with, said shaftl.

Other objects and many of the attendant advantages of the present invention will become more readily apparent by reading the following detailed description with reference to the accompanying drawings wherein:

FIG. 1 is a longitudinal sectional view of a multi-turn potentiometer embodying the present invention;

FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1;

I FIG. 3 is an exploded isometric view of the multi-tur'n potentiometer illustrated in FIG. 1; and

FIG. 4 is a bottom perspective view of a terminal plate which forms part of the illustrated invention.

The present invention comprises a casing generally identified by the numeral 2 which comprises two complementary parts 4 and 6. The part 4 comprises a semieylindrical Wall 8 and a single end Wall 10. End wall 10 is semi-cylindrical in shape, but includes a centrally located portion 12 which is of semi-cylindrical shape and which cooperates with the remaining portion of end wall 10 to define a central opening 14.

The internal surface of semi-cylindrical wall 8 is formed with parallel grooves 16 which together comprise one half of a continuous spiral groove. In addition, the semi-cylindrical casing part 4 has a slot 20 formed along one edge of the semi-cylindrical surface 8. The semicylindrical surface 8 is provided with a raised flange 22 which runs along the edge of slot 20. In addition the longitudinal edges of the semi-cylindricalsurface 8. and the corresponding edge of the end wall 10 are provided With a continuous ridge 24.

The other part 6 has a semi-cylindrical'wall 26 and an end wall 28, the latter is formed with a semi-cylindrical opening 30 at its center. The radius of opening 30 is the same as the radius of the semi-cylindrical section 12 formed integral with the end wall 10 of the other section 4. Thus when the two sections are put together the portion 12 will nest in and fit tightly against the semicylindrical opening 30. The longitudinal edges of the semi-cylindrical wall 26 of casing part 6 are formed with a groove 34 (see FIG. 2) which is complementary to the ridges 24 on the other casing part 4. It is to be noted that groove 34 also extends along the surface which defines the semi-cylindrical opening 30. In thisway, when the two casing sections are put together, the semicylindrical portion 12 will be locked to the other casing section by virtueof the engagement made by the ridge 7 24 of portion 12 with the groove 34 along'the surface v The external diameter of bushing 48 varies, its outer sur which defines the opening 30.

the other casing section 6. Slot 36 is the mirror image of slot 20 of the other casing sectionand i provided with a raised flange 38 which is identical and complementary to the raised flange 22 which borders the slot 20. Incidentally, it is to be noted also that the end wall 10 of the casing section 4 is provided with a partially embedded pin 40 and that, end wall 28 of the other casing section is formed with a semi-circular opening 42 sized to receive the exposed portion of pin 40. Pin 40 is a locating pin and, as is well known to persons skilled in the potentiometer art, locating pins are used so as to facilitate positioning of the potentiometer. when it is being attached to a supporting assembly. 1

I The central opening 14 receives'a bushing 48. The internal diameter of bushing 48 is substantially constant and is slightly largerthan the external diameter of an operating shaft 50 which is positioned within the bushing.

face comprising two threaded portions 52 and 54 with the threaded portion 52 being. longer than the threaded portion 54. The threaded portion 52 is also of greater diameterthan the threaded portion 54. These two threaded portions are separatedby an unthreaded stepped see 4 tion generally identified by the numeral 56. The outer diameter of the threaded portion 54 is the same as the largest diameter of the unthreaded stepped portion 56. This diameter is slightly smaller than the hole 14 formed in the end wall all of a casing section 4. The junction between the stepped portion 56 and the threaded portion 48 forms a shoulder When the bushing is inserted in the opening 14 the shoulder 53 engages the inner surface of the end wall 16, as shown in FIG. 1. The threaded portion 54 serves two purposes: (1) to act as a threaded bushing extension on the front-end portion of the potentiometer for panel mounting and (2) to receive a nut 60. When nut 61; is screwed onto the threaded portion 54, it will draw the shoulder 53 tight against the inside surface of the end wall 16 so as to prevent rotational or longitudinal movement of the bushing.

Shaft 56 is of stepped construction, having a reduced diameter for a substantial portion of its length intermediate its ends as indicated generally at 62 in FIGS. 1 and 3. This reduces the friction between shaft 56 and the interior of the bushing.

The rear end of shaft 56 is slotted as indicated at 64. This slot 64 is sized to accommodate a U-shaped element 66 comprising a pair of arms 68 and 70 and a connecting portion 72. The portion 72 resides in the slotted portion 64 of shaft 5%). A pin 74 (FIG. 1) passing through suitable openings in the shaft 50 and the connecting portion 72 functions to hold the U-shaped element 66 to the shaft. The connecting portion 72 is seated fully in slot 74. Accordingly the bottom of the slot cooperates with pin 72 so as to eliminate any movement of the U-shaped element relative to shaft 50. The two arms 68 and 7t) extend parallel to the threaded portion 52 of bushing 48 but terminate short of shoulder 58. Thus when the bushing is mounted within the housing and the shaft with U- shaped element 66 attached thereto is inserted in bushing 48, the ends of arms 68 and 76 will not engage the end walls It and 28; nor will they engage the surrounding cylindrical Wall of the housing. Interposed between the U-shaped element 66 and the end of bushing 48 is a pair of washers 76 and 78 which are spaced apart by a con cave spring washer Sil. When the U-shaped element 66 is slipped onto the shaft, sufiicient pressure must be exerted thereon so as to distort spring washer 80. Once the U-shaped element 66 is pinned to the shaft, spring washer 80 will be prevented from returning to its normal unfiexed position. As a consequence, it will retain the washer 73 flush against the end surface of bushing 48 and will retain the other washer 76 flush against the connecting section 72 of the Ll-shaped element 66. This prevents shaft 50 from moving longitudinally toward the reduced end of the bushing 48. Opposite movement of shaft Ed is prevented by a G-ring 84 which is slipped into a suitable groove formed in shaft 50 just in advance of the forward end of the bushing 48. The friction exerted by the C-ring 84 on the end of the bushing 48, like the friction exerted by washers 76, 8t and 78 against the U- shaped element 66 and the other end of bushing 48, is insufiicient to prevent easy rotation of shaft 50.

The bushing also accommodates a special nut 88. As seen in FIGS. 1 and 3, the nut is provided with diametrically opposed longitudinally extending slots Q6 and 92 having a width just sufficient to accommodate the arms 68 and 76 as illustrated in FIG. 1. On its opposed faces the nut 88 has projections 94 and 96. These projections are provided to engage stop pins 98 and 100 which are force fitted into radial bores formed in bushing 48. Stop pins 98 and flit) do not extend radially a distance sufficient to interfere with rotation of the arms 68 and '70. However, they are spaced apart a distance sufficient to limit rotation of shaft 50 and nut 88 to a predetermined number of turns. In the usual case the number of turns is ten.

Attached to the connecting portion 72 of U-shaped element 66 is a spring contact element 1%. This spring contact element is secured to the outer surface of connecting surface 72 by means of a rivet 166 which also passes through a washer 1.6 3. As shown in FIGS. 1 and 3, contact element tea has two arms 116 which are provided with rounded projections 112. When the element 66 rotates, the contact id-twill rotate with it. Conductively secured to the contact 104 is a flexible insulated wire 114-. The latter extends around one of the arms of U-shaped element 66 and is attached to a resilient contact 118 which is secured to nut 83 by means of a screw llZh. Resilient contact 118 projects laterally away from the nut towards the interior surface of the casing 4 and at its free end it engages a helical resistance element 124 which is mounted within the casing.

it is to be observed that the bushing, the shaft, the U- shaped element 66, the nut 88, and the elements which are carried thereby including contacts liteand 118, are all attached to the casing section 4 prior to insertion of the resistance element 12 and the application of the second casing section 6. The resistance element is slipped over U-shaped element 66 and then is adhesively secured to casing section 4 by application of a suitable conventional adhesive to grooves 16. In this connection it is to be noted that additional grooves 128 are provided in casing section 6. These grooves, like grooves 16, are sized to accommodate resistance element 124. Accordingly, when the two casing sections are placed together, resistance element 124 will be captivated by the two casing sections so that it will be incapable of movement relative to the casing. Additional adhesive applied to grooves 128 prevents rotation of the resistance element.

After the casing sections have been secured together, and this is done by means of an adhesive which is applied to the facing edges of the two casing sections, electrical contacts are made to the resistance element. Wire leads are soldered to opposite ends of the resistance element 124 at portions thereof which are exposed through the opening formed by the matching slots 29 and 36. After this is accomplished, a terminal plate 134 is attached to the casing so as to hide the opening formed by slots 20 and 36. Details of the plate 134 are illustrated in FIGS. 2, 3 and 4. It is to be observed that this plate is essentially of rectangular construction. However, on its bottom surface it is provided with a generally elliptical groove 136 having a depth and width sized to accommodate ribs 22 and 38. Thus the terminal plate can be secured to the casing only in a predetermined position. A conventional cement is used to attach the plate to the casing. Plate 134 is provided with at least two holes 142 and 144, the accommodate rivets (not shown) which are used to anchor external L-shaped terminals 156 and 152 to the cover plate. The wire leads previously soldered to the resistance element 124 are soldered to the aforesaid rivets on the bottom side of plate 134. In this manner electric current may be coupled to the resistance element via contacts 152 and 154.

The terminal plate 134 is also formed with a notch 158 at its rear end. The purpose of notch 158 is to accon modate a collector terminal 160. Each of two casing sections 4 and 6 is also formed with a depression 162 at the edge opposite the slots 2t? and 33 so as to accommodate the opposite end of the collector terminal 168. In this respect it is to be noted that the opposite end of collector terminal 169 is offset as shown at 16 2 so as to fit snugly within the depressions 162. Having an offset portion not only helps locate the collector terminal but also prevents it from shifting axially along the casing toward end walls 10 and 28. It will be observed that the collector terminal 166 has a generally annular section 166 intermediate its ends. The function of this annular section 166 is to act as a riding surface for the rounded projections 112 on the ends of arms of contact 104. The collector terminal 16f? thus acts as a take-off terminal for the voltage which is picked up by the contact 118 from the resistance elelarged portion of cover 170 is equal to the outside diameter of the casing. Thus when the cover is inserted in the casing, the outer surface of the cover will be flush with the outer surface of the casing. The reduced diameter section 172 is formed with a series of spiral ridges 176 p which mate with complementary grooves 178 formedon the inside surface of the two casing sections. When the cover is to be inserted in the casing, it is necessary to screw it in so that the ridges 176 will mate and lock with the cooperating grooves 178. It is to be observed that the end cover section has a slight radial projection 180. When the end cover is locked tight, projection 180 is in direct alignment with the adjacent end of cover 134. Thus the end of collector terminal 160 will be sandwiched therebetween and will thereby be supported against bending in the region where it projects from the housing.

It will be readily appreciated from the foregoing description and the accompanying drawings that the present invention has many advantages over prior multi-turn potentiometers. For one thing, it is possible to use a plastic case without at the same time forming or molding the plastic case directly about the resistance element. This eliminates a costly and complex molding procedure. On the other hand, due to the fact that the end wall 10 has a portion 12 which forms a centrally located hole 14, the illustrated construction is capable of providing a suitable anchor for the bushing 48. The rigidity obtained by this construction is not obtainable with prior constructions of the type where the casing consists of two fully identical half sections.

A further advantage of the present invention resides in the slots and 38 which permit'the use of a removable terminal plate 134. In this manner electrical connections to the resistance element are greatly facilitated and may be accomplished after the resistance element is located within the casing.

Another important advantage of the present invention is that it is cheap and inexpensive to manufacture. The

casing may be made of inexpensive plastic; so also may the terminal plate 134- and the end cover 170. In the same manner the nut 88 may be made of nylon or Teflon so as to rotate easily on the bushing 48. The U-shaped element 66 may be made of metal or plastic. It need not be conductive since it is not intended to function as an electrical conductor. Of course, both the operating shaft 7 and the bushing 48 may be made of conductive or nonconductive materials, such as steel, aluminum, or plastic.

It is to be noted that the cover plate 134 may be provided with more than two holes. In the illustrated embodiment, a knock-out 188 is shown intermediate the two holes 142 and 144. 'The purpose of having a knock-out is to allow the use of an additional terminal for connection to the resistance element so as to take off intermediate voltages. Although only one knock-out is shown, it is to be understood that additional knock-outs may be provided if desired.

Obviously many variations and modifications of the present invention'will readily suggest themselves to per sons skilled in the art. Accordingly this invention is not to be restricted except by the followingjclaims.

We claim: I

l. A multi-turn potentiometer comprising a cylindrical housing formed in two matching parts, each part comprising a semi-cylindrical side wall and an end wall, the

end wall of one part having a semi-circular slot disposed in coaxial relation to said side wall of said one part, the

s end wall of the other part having a semi-circular projection disposed so as to fit in and fully occupy. said slot when said two parts are placed together, said end wall of said other part also having a central opening, and means for supporting an operating shaft in said central opening. 7

2. A multi-turn potentiometer as defined by claim 1 wherein said two parts are provided with slots along corresponding longitudinal edges of said side walls, and a terminal plate attached to said side walls in covering relation to said slots.

3. A multi-turn potentiometer as defined by claim 1 wherein said two parts have contacting edges which provide a tongue-and-groove construction, whereby to automatically locate said parts in matching relation 'to each other.

4. A multi-turn potentiometer as defined by claim 1 further including an end closure screwed into said housing at the end opposite said end walls, and a terminal element held within said housing by said closure member, a portion of said terminal element projecting outside of said housing for connection to an external electrical circuit.

5. A multi-turn potentiometer as defined by claim 1 wherein said central opening is located in said projection.

6. A multi-turn potentiometer as defined by claim 2 wherein said side walls and said terminal plate are connected by'a tongue-and-groove construction.

.7. A multi-turn potentiometer as defined by claim 2 wherein said terminal plate is provided with a terminal element adapted to be conductively connected to a resistance element contained within said housing.

8. A multi-turn potentiometer comprising a cylindrical housing, a helical resistance element positioned within said housing, a bushing coaxially mounted in an end wall of said housing, said bushing having an externally threaded portion extending within said housing, a nut on said externally threaded portion, a resilient conductive contact having one end secured by said nut and the other end in slidable engagement with said resistance element,

'an operating shaft rotatably disposed within said bushing, said shaft having its inner end projecting beyond the inner end of said bushing, and a yoke connecting said inner endnf said shaft and said nut for rotating said nut with said shaft, whereby said resilient contact will travel along the-turns of saidresistance element.

9. A potentiometer as defined by claim 8 further including a conductive element secured to said yoke for rotation therewith, said conductive element having a resilient contact portion spaced from said yoke, a stationary conductive collector slidably engaged by said resilient contact portion at all times, and means electrically connecting said resilient contact and said conductive element whereby to couple a signal picked up by said contact to said collector.

l 0. A potentiometer as defined by claim 9 wherein said housing has a removable end cover plate and said stationary collector is located adjacent to said cover plate in longitudinal spaced relation to said yoke.

11. A multi-turn potentiometer comprising a cylindrical casing formed in two parts, one part having an end wall which comprises a major portion having theshape of one half of a relatively large annulus and a minor portion having the shape of one half of a relatively small annulus, said major and minor portions defining a central opening, the other part of said casing having an end wall provided with a semi-circular opening sized to accommodate said minor portion, both of said casing sections having matching edge elements providing interlocks so as to eliminate relative movement between the two casing sec- 7 tions, a helical resistance element mounted within said casing, a bushing mounted within said central opening, said bushing having an externally threaded portion within said casing, a shaft mounted within said bushing for rotation relative to said bushing, a nut on the externally A threaded portion of said bushing, means on said shaft for rotating said nut on said bushing whensaid shaft is rotated, a resilient contact carried by said nut and normally acanaaa in engagement with said resistance element, said resilient contact movable with said nut as said nut is rotated by said shaft, means for applying a voltage to said resistance element, and means for removing the voltage picked off of said resistance element by said resilient contact.

12. A multi-turn potentiometer as defined by claim 11 wherein said two casing sections are formed with mating longitudinally extending slots along adjacent edges and means for covering said slots, said covering means including a pair of terminals for connection to said resistance element adjacent its opposite ends.

13. A potentiometer comprising a cylindrical housing formed in two matching parts, each part comprising a side wall and an end wall having an edge free of said side wall, the end wall of one part having a slot along one portion of its edge, the end wall of the other part having a projection shaped to occupy said slot and interlock with the end wall of said one part when said two parts are placed together, said projection having an opening, an operating shaft for said potentiometer, and means supporting said shaft in said opening.

14. A potentiometer as defined by claim 13 wherein said side walls have interlocking portions along their longitudinal edges.

15. A potentiometer as defined by claim 13 further including a removable end cover plate screwed into said housing at the end opposite to said end walls.

16. A potentiometer as defined by claim 15 further including a stationary conductive terminal projecting out of said housing and secured to said housing by said end cover plate.

References Cited in the file of this patent UNITED STATES PATENTS 2,815,422 Lock Dec. 3, 1957 2,871,326 Weidenman et a1 I an. 27, 1959 2,887,555 Marason May 19, 1959 2,945,199 Mucher et a1 July 12, 1960 

